Unsaturated nitrile polymers stabilized by substituted melamines and phenols



United States Patent 3,316,208 UNSATURATED NITRILE POLYMERS STABILIZED BY SUBSTITUTED MELAMINES AND PHENOLS Yoon Chai Lee and Speros P. Nemphos, Springfield, Mass, assignors to Monsanto Company, a corporation of Delaware No Drawing. Filed Sept. 23, 1963, Ser. No. 310,892 12 Claims. (Cl. 260-45.8)

This invention relates to unsaturated nitrile polymers and more particularly relates to the stabilization of such polymers against discoloration.

The presence of a combined unsaturated nitrile, such as acrylonitrile, methacrylonitrile, etc., in a polymer is known to contribute valuable properties to the polymer. However, as is well known, the unsaturated nitrile present in the polymer has a tendency to discolor it, particularly when the polymer is subjected to the elevated temperatures required formolding and extrusion operations.

An object of the invention is to provide novel unsaturated nitrile polymer compositions having a reduced tendency toward discoloration.

Another object is to provide processes for stabilizing unsaturated nitrile polymers against discoloration.

These and other objects are attained by intimately mixing an unsaturated nitrile polymer (i.e., a polymer containing at least by weight of a combined unsaturated nitrile of the group consisting of acrylonitrile, methacrylonitrile, ethacrylonitrile, propacrylonitrile, butacrylonitrile, and mixtures thereof) with about ODDS-0.1%, based on the weight of the polymer, of a stabilizer which corresponds to the formula:

wherein one R represents a member of the group consisting of -CH CH OH, --C'H CHO-HCH CH OCH and CH OCH C'H and the remaining Rs are independently selected from the group consisting of -H, C-H CH O H, CH CHOHCH -OH OCH and -CH OC'H CH The following examples are given to illustrate the invention. Unless otherwise specified, quantities mentioned are quantities by weight.

EXAMPLE I Part A (control) Dissolve about 0.03 part of di-t-butyl peroxide in a monomer mixture consisting of 70 parts of styrene and 30 parts of acrylonitrile. 'Purge the reaction vessel with nitrogen. Heat the reaction mixture at 125 C. for 3 hours and at 140 C. for 3.5 hours to form a styrene/ acrylonitrile copolymer. Age the copolymer at 200 C. for 6 hours.

Part B Prepare two aged styrene/ac'rylonitrile copolymers by repeating. Part A except for also dissolving, respectively, (1) 0.04 part of hexa(methoxymethyl)melamine (HMMM) and (2) 0.04 part of HMMM and 0.02 part of 2,6-di-t-butyl-p-cresol (DTBPC)in the monomer mixtures.

Part C Determine the stabilizing eifects of the additives of Part B by 1) dissolving 2 grams of each of the copolymers of Parts A and B in 50 ml. of chloroform, (2) measuring the percentage of light transmitted through each of the solutions at 380 mu, 400 mu, and 420 mu, (3) calculating the stabilizing effects of the additives in accordance with the equations:

Stabilizing effect (380 mu)= ;Z)

Stabilizing efl ect 400 mu)= l iw Stabilizing effect 420 mu g wherein Z, X, and V represent the percentages of light transmitted through the solution of the copolymer of Part A at 380 mu, 400 mu, and 420 mu, respectively, and Y, W, and U represent the percentages of light transmitted through a solution of a copolymer of Part B at 380 mu, 400 mu, and 420 mu, respectively, and (4) calculating the average of the three stabilizing effects of each additive. The average stabilizing effects of the additives of Part B are shown below.

Additive: Stabilizing effect 0.04 HMMM 29 0.04 HMMM/0.02 DTBPC 223 EXAMPLE II Part A (control) Charge 200 parts of water, 67 parts of styrene, 33 parts of acrylonitrile, about 0.03 part of di-t-butyl peroxide, and about 003 part of a water-soluble acrylic acid/2- ethylhexyl acrylate (93.21618) copolymer to a suitable,

agitated reaction vessel. Pressurize the reaction mixture with nitrogen and heat at 150 C. for about 8 hours to copolymerize the monomers. Filter, and then wash and dry the styrene/acrylonitrile copolymer beads.

Part B Prepare two styrene/acrylonitrile copolymers by repeating Part A except for also including, respectively, (1) 0.01 part of hexa(methoxymethyl)melamine (HMMM) and 002 part of 2,6-di-t-butyl-p-cresol (DTBPC) and (2) 0.005 part of HMMM and 0.02 part of DTBPC in the charge to the recation vessel.

C., tw ice re-extruding at 260 C., and injection molding the extruded pellets at about 200 C. Measure the reflectance of light of each of the specimens at 700 mu, 500 mu, and 420 mu, and calculate the three-point yellowness of the specimen in accordance with the equation:

wherein SPY represents the three-point yellowness value and R R and R represent the reflectances at 700 mu, 500 mu, and 420 mu, respectively.

Part D Calculate the color stabilizing effects of each of the additives of Part B in accordance with the equations:

Z Stabilizing effect I:

X Stabilizing effect II= wherein Y and W represent the respective three-point yellowness values of specimens I and II of the copolymer of Part A, and Z and X represent the respective threepoint yellowness values of specimensI and II of a copolymer of Part B. The color stabil1z1ng eifects of the additives are shown below.

Stabilizin Stabilizing Addmve Effect l Effect II fi 0.01 HMMM/0.02 DTBIC 35 39 0.005 I-IMMM/002 DIBPQ-.. 40 -8 Part E Calculate the diiference 'between the three-point yelloiwness values of specimens I and II of each of the copol ymers of Parts A and B. Then determine the heat stabilizing effect of each of the additives of Part B in accordance with the equation:

1 YZ Heat stabilizing eiiect= wherein Y represents the difference between the threepoint yellowness values of specimens I and of the copolymer of Part A, and Z represents the difference between the three-point yellowness values of specimens I and II of a .coplymer of Part B. The heat stabilizing efiects of the additives are shown below.

Additive: Heat stabilizing effect 0.01 HMMM/0.02 DTBPC 21 0.005 HMMM/0.02 DTBPC 12 As demonstrated in the preceding examples, hexa (methoxymethyl)melamine is effective in stabilizing u nsaturated nitrile polymers against discoloration, and its effectiveness is enhanced by employing it in conjunction with an alkylphenol. Similar results are observed When:

(1) The stabilizer is intimately mixed with a preformed unsaturated nitrile polymer instead of being incorporated into the monomer charge employed in preparing the 1msaturated nitrile polymer,

(2) The polymer being stabilized is po lyacrylomtrile, poly-methacrylonitrile, a styrene/acrylonitrile (50:50) copolymer, a styrene/methacrylonitrile (85:15) copolymer, an alpha-methylstyrene/acrylonitrile (80:20) copolymer, a styrene/alpha-methylstyrene/acryloni-trile (50:40:10) terpolymer, or a styrene/acrylonitrile/N-t-butyl acrylamide (70:20:10) terpolymer, g

(3) The hexa(methoxymethyl)melamine is replaced with 0.005-0.1 part of hexa(beta-hydroxyethyl)rnelamine, tetra(beta hydroxypropyl)melamine, methoxymethylmelamine, or di(ethoxymethyl)melamine, or

(4) The 2,6-di-t-butyl-p-cresol is replaced with 0.01- 0.1 part of 2,2'-methylene bis(6-t-butyl-p-cresol), 4,4- butylidene-bis (6-t-butyl-rn'cres0l) 2-t-butyl-4-phenylphenol, 2,6-dibenzyl-p-cresol, 2,6-diisopropylphenol, 2-tbutyl-p-cresol, or 2,6-di-t-butylhydroquinone.

The polymers which are stabilized in accordance with the present invention are unsaturated nitrile polymers, i.e., polymers containing at least 10% by weight of a combined unsaturated nitrile of the group consisting of acrylonitrile, methacrylonitrile, ethacrylonitrile, propacrylonitrile, butacrylonitrile, and mixtures thereof. Exemplary of such polymers are the homopolymers of these unsaturated nitriles, i.e., polyacrylonitrile, polymethacrylonitrile, etc.; interpolymers of two or more of these unsaturated nitriles, e.g., acrylonitrile/methacrylonitrile copolymers, acrylonitrile/methacrylonitrile/ethacrylonitrile terpolyrners, etc.; interpolymers of at least 10% by weight of one or more of these unsaturated nitriles with up to by weight of one or more copolyrnerlizable monomers such as a monovinylidene aromatic hydrocarbon (e.g., styrene; an ar-alkylstyrene such as the 0-, m-, and p-methylstyrenes, 2,4-dimethylstyrene, \ar-ethylstyrenes, p-t-butylstyrene, etc.; an alpha-alkylstyrene such as alphamethylstyrene, alpha-ethylstyrene, alpha-methyl-p-methylstyrene, etc.; vinyl naphthalene; and mixtures thereof), an alkyl (alk)acrylate (e.g., methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, the corresponding alkyl methacrylates, etc., and mixtures thereof), an acrylamide (e.g., acrylamide; methacrylamide; an N-alkyl acrylamide such as N-methyl acrylamide, N-butyl acrylamide, etc.; and mixtures thereof), dialkyl maleates and fumarates (e.g., diethyl maleate, dibutyl fumarate, etc., and mixtures thereof), etc. Many other unsaturated nitrile polymers which contain at least 10% by weight of a combined unsaturated nitrile and which present a discoloration problem because of their unsaturated nitrile content will be obvious to those skilled in the art.

A preferred embodiment of the invention is its application to the stabilization of acrylonitrile polymers, particularly monovinylidene aromatic hydrocarbon/acrylonitrile interpolymers containing about 1550% by weight of combined acrylonitrile. Such interpolymers include those which contain no combined monomers other than acrylonitrile and one or more monovinylidene aromatic hydrocarbons as well as those which also contain a minor amount, e.g., up to about 20% by weight, of one or more combined comonomers such as the alkyl (alk) acrylate, acrylamide, and dialkyl maleate and fumarate comonomers exemplified above.

The stabilizers of the invention are compounds which correspond to the formula:

wherein one R represents a member of the group consisting of CI-I CH OH, -CH CHOHCH -CH OCH and CH OCH CH and the remaining Rs are independently selected from the group consisting of H,

and -CH OCH CH Exemplary of such compounds are the mono-, di-, tri-, tetra-, penta, and hexa(n1ethoxymethyl)melamines, the corresponding 'beta-hydroxyethyl beta-hydroxypropyl-, and ethoxymethylmelamines, and

mixtures thereof. The hexa-substituted melamines', especially hexa(methoxymethyl)melamine, are preferred. The amount of stabilizer employed should be in the range of about 0.005-0.1%, preferably about 0.005-0.05%, based on the weight of the unsaturated nitrile polymer.

The alkylphenols which can be used in conjunction with the stabilizers of the invention are aromatic compounds which have at least one hydroxyl group and at least one alkyl group attached to a benzene nucleus. When used, the alkylphenols are ordinarily employed in concentrations'of about 0.010.1%, based on the weight of the unsaturated nitrile polymer. Up to about of an alkylphenol may be employed when it is mixed with a preformed unsaturated nitrile polymer, but these higher concentrations of alkylphenol are usually undesirable when it is incorporated into a monomer charge which is to be polymerized to form an unsaturated nitrile polymer. Alkylphenols suitable for use in conjunction with the stabilizers of the invention include, e.g.:

2,2-methylene-bis 6-t-butyl-p-cresol) 2,2'-methylene-bis 6 -t-butyl-4-ethylphenol 2,2-methylene-bis [4methyl-6-( 1,1,3,3-tetramethylbutyl)- phenol] 4,4-thio bis (6-t-butyl-m-cresol) 4,4-butylidene-bis G-t-butyI-m-cresol) 2,2-methylene-bis (4,6-dimethylphenol) 2-t-butyl-4- (4-t-butylphenyl phenol 2 t-butlyl-4-phenylphenol 2,6-dibenzyl-p-cresol 2,6-dibenzyl-p-cresol 2-benzyl-p-cresol 2-benzyl-6-t-buty1-p-cres ol 2-benzyl-6-t-butyl-4-ethylphenol 2,4-dimethyl-6- 1 -methyl- 1 -cyclohexyl phenol 2,6 -diisopropyl-p-cresol 2,4-dimethy1-6-isopropylphenol 2-t-butyl-4,6-dimethylphenol 2-t-butyl-p-cresol 2-(1,1,3,3-tetramethylbutyl)-p-cresol 2,4,6-trimethylphenol 2,6-di-t-butyl-p-cresol 2,6di-t-butyl-4-ethylphenol 2, fi-diisopropylphenol 2,6-di-t-butyl-4-phenylphenol 2,6-dir-t-butyl-4- 4-t-butylphenyl phenol 2, 5 -di-t-butylhydro quinone 2,5-di-t-amylhydroquinone, etc.

The stabilizers of the invention and the alkylphenols, when employed, can be incorporated into the unsaturated nitrile polymers by any technique which permits their uniform distribution throughout the polymers, e.g., by blending them with preformed unsaturated nitrile polymers on a two roll mill or other suitable mixing device, by adding them to the monomer charge which is to be polymerized to form an unsaturated nitrile polymer, etc. According to a preferred embodiment of the invention, the stabilizer and the alkylphenol, when employed, are added to a polymerizable material containing at least by weight of an unsaturated nitrile, and the polymerizable material is then polymerized by any desired conventional technique, e.g., by heating the polymerizable material at a temperature in the range of about 50-200 C. using a mass, solution, emulsion, suspension, batch, or continuous polymerization technique.

When desired, the stabilized compositions of the invention can contain optional additives such as plasticizers, lubricants, colorants, rubbery polymers, etc., which are sometimes added to the polymeric compositions and, in other cases, e.g., when grafting onto a rubber backbone is desired, are incorporated into the polymerizable material comprising the unsaturated nitrile.

The stabilized compositions of the invention have the obvious advantage of being characterized by a reduced tendency toward discoloration and have the additional 6 advantage that-because of the water-insolubility of the stabilizersobjects formed from the compositions can undergo prolonged exposure to water without suffering from stabilizer leaching.

It is obvious that many variations can be made in the products and processes set forth above without departing from the spirit and scope of this invention.

What is claimed is:

1. A composition which comprises an interpolymer of a monovinylidene aromatic hydrocarbon and an unsaturated nitrile polymer, said interpolymer containing 10- by weight of a combined unsaturated nitrile of the group consisting of acrylonitrile, methacrylonitrile, ethacrylonitrile, propacrylonitrile, butacrylonitrile, and mixtures thereof in intimate admixture with 0.0l-5.0% by weight of an alkyl phenol and about ODDS-0.1%, based on the weight of the polymer, of a stabilizer corresponding to the formula:

wherein one R represents a member of the group consisting of -CH CH OH, -CH CHOHCH -CH OCH and -CH OCH CH and the remaining Rs are independently selected from the group consisting of H, CH CH OH, -CH CHOHCH CH OCH and CH OCH CH 2. The composition of claim 1 wherein unsaturated nitrile is acrylonitrile.

3. The composition of claim 1 wherein the unsaturated nitrile polymer is a mon-ovinylidene aromatic hydrocarbon/acrylonitrile interpolymer containing about l5-50% by weight of combined acrylonitrile.

4. The composition of claim 3 wherein the monovinylidene aromatic hydrocarbon/acrylonitrile interpolymer is a styrene/acrylonitrile copolymer.

5. The composition of claim 3 wherein the monovinylidene aromatic hydrocarbon/acrylonitrile interpolymer is an alpha-mothylstyrene/acrylonitrile copolymer.

6. The composition of claim 3 wherein the monovinylidene aromatic hydrocarbon/acrylonitrile interpolymer is a styrene/alpha-methylstyrene/acrylonitrile terpolymer.

7. The composition of claim 1 wherein the stabilizer is hexa (methoxymethyl melamine.

8. The composition of claim 1 wherein. the concentration of the stabilizer is in the range of about 0.0050.05% based on the weight of the polymer.

9. The composition of claim 1 wherein the alkylphenol is 2,6-di-t-butyl-p-cresol.

10. A composition which comprises a monovinylidene aromatic hydrocarbon/acrylonitrile interpolymer containing about 1550% by weight of combined acrylonitrile in intimate admixture with about 0.0l0.l% by weight of 2,6-di-t-butyl-p-cresol and about ODDS-0.05% by weight of hexa(methoxymethyl)melamine.

11. The composition of claim 10 wherein the monovinylidene aromatic hydrocarbon/acrylonitrile interpolymer is a styrene/acrylonitrile copolymer.

12. A process which comprises dissolving about 0.0l 5.0% by weight of an alkylphenol and about 0.005-0.l% part by weight of a stabilizer in parts by weight of a polymerizable material containing a monovinylidene aromatic hydrocarbon and 1090% by weight of an unsaturated nitrile of the group consisting of acrylonitrile, methacrylonitrile, ethacryl-onitrile, propacrylonitrile, butacry-lonitrile, and mixtures thereof and heating to polymthe combined 7 8 erize the polymerizable material; said stabilizer being -CH CH OH, CH CHOHCH CH OCH and a compound Which corresponds to the formula: CH OCH CH R N R i References Cited by the Examiner 5 UNITED STATES PATENTS r 2,804,444 8/1957 Segro et a1 260-4595 e 1 3,189,569 6/1965 Finestone 260-45.95

N FOREIGN PATENTS 10 wherein one R represents a member of the group consist- 92O146 11/1954 Germany ing Of CHgCHgOH, CHQOCHE, 3 I and CH OCH CH and the remaining Rs are indepen- LEON BERCOVITZ Examme" ,dently selected from the group consisting of H, M. J. WELSH, Assistant Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,316,208 April 25, I967 Yoon Chai Lee et al.

ed that error appears in the above numbered pat- It is hereby certifi said Letters Patent should read as ent requiring correction and that the corrected below.

Column 6 line 11 strike out "polymer".

Signed and sealed this 31st day of December 1968.

(SEAL) Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer 

1. A COMPOSITION WHICH COMPRISES AN INTERPOLYMER OF A MONOVINYLIDENE AROMATIC HYDROCARBON AND AN UNSATURATED NITRILE POLYMER, SAID INTERPOLYMER CONTAINING 1090% BY WEIGHT OF A COMBINED UNSATURATED NITRILE OF THE GROUP CONSISTING OF ACRYLONITRILE, METHACRYLONITRILE, ETHACRYLONITRILE, PROPACRYLONITRILE, BUTACRYLONITRILE, AND MIXTURES THEREOF IN INTIMATE ADMIXTURE WITH 0.01-5.0% BY WEIGHT OF AN ALKYL PHENOL AND ABOUT 0.005-0.1%, BASED ON THE WEIGHT OF THE POLYMER, OF A STABILIZER CORRESPONDING TO THE FORMULA: 